A novel, self-correcting membrane coating technique

A novel coating process, leading to formation of uniform, defect-free coating on solid dosage forms, is proposed. The coating process, termed "diffusion-controlled interfacial complexation," involves a chemical reaction between a reactant incorporated in the solid unit to be coated and a polymer solution, forming the coating medium. The reaction results in the formation of an insoluble reactant-polymer film around the solid. The rate of film/membrane formation is controlled by the rate of diffusion of reactant through the reactant-polymer film. In the model system, calcium acetate was selected as the reactant and algin as the polymer. The coating process was mathematically characterized in terms of rate of increase in film thickness, film weight, and depletion of reactant. Compressed tablets coated using the above process provided zero-order release in distilled water.